Tank flushers that comprise, as main constituent elements of the same, a hood inside of which there is a valve that closes upon the flushing inlet of the tank and that is displaced by traction, are known in prior art. The valve in question is integral with a rod generally tubular, that acts as an overflow tube. In the same way, in the so-called "low tanks," this is produced by traction but a float fastened on the overflow tube is included.
The operation of this type of the so-called hydropneumatic flushers is done by establishing a connection of the air chamber of the hood, with the atmosphere, through a duct provided in the end of a plug, operated by pushing, in such a way that a depression is produced in said chamber by a release of air, permitting the elevation of the float, by the water pressure, which pulls by traction the plug valve which opens the bottom inlet of the tank, causing the total flushing of the liquid that it contains.
In order to effect successive flushings it is necessary to wait, for the same have been carried out, until the float and valve drop to the closing position, in order for the tank to fill up.
Flushers of the type described also pose the problem that if upon establishing the communication of the air chamber with the outside, there is not enough water in the tank, there is a partial elevation of the valve pulled by the float, which insufficiently raises the plug rubber, producing a slight opening of the flusher inlet, thus, the water of the tank spills in the same proportion as it arrives through the filler duct, thus, the flusher remains nonusable, upon producing its balance between the water flow that enters and that which comes out of the tank.
Generally, in the cited case, the valve never recovers and the plugging system has to be operated by hand, which requires the air of an expert.